The present invention involves optical devices and methods for detecting coded symbols, particularly optical devices for reading bar codes and other symbols representing data.
Bar codes are increasingly used on products and other objects to encode information in machine readable forms. A bar code containing encoded information is placed on the object. The bar code may be read by use of a bar code reader or scanner which uses an optical method to read the bar code.
A variety of bar code languages, or symbologies, are presently in use. Although early symbologies were one dimensional, that is they encoded information in one dimension only, two-dimensional bar code symbologies are becoming increasingly popular due to the growing desirability to encode increasing amounts of information in smaller and smaller spaces. Examples of different types of two-dimensional bar codes include stacked symbologies (e.g., linear bar codes stacked on top of each other), matrix symbologies (e.g., a matrix of light and dark elements, circles, squares, or hexagons), or packet symbologies (e.g., a collection of linear symbols which appear to be randomly arranged on a page). Examples of the three types include, respectively, PDF417, Code 49, and Code 16K (stacked); Code One, MaxiCode, Data Matrix, Aztec Code, and QR Code (matrix); and Super Code (packet).
An exemplary application for two-dimensional bar codes is on singly-packaged cigarettes, which have bar code information placed thereupon to verify that the required taxes have been paid. The surface area for bar codes on such packaging is rather small, and, therefore, two-dimensional bar codes are useful to provide a large amount of information in a small space. Other uses of bar codes include price information, information useful to discover counterfeiting, model or manufacturing information, and many others.
Along with their advantage of enabling storage of vast amounts of data (data and information may be used interchangeably and substantially equally herein), two-dimensional bar codes have the disadvantage of introducing some difficulties in bar code reading. Although some stacked two-dimensional codes can be read with a rastering laser system, most two-dimensional symbologies require a vision-based reader to read the encoded data.
In such a vision-based reader the bar code is illuminated by a light source and the resulting image is focused on an array of photodetectors such as charge coupled devices (CCDs). An electrical signal is applied to the CCD array and the light value at each photodetector is read. This signal is processed and decoded to reveal the information encoded in the bar code.
Non-uniform illumination can cause difficulties for vision-based readers in that the non-uniform illumination leads to readings by the photodetectors which do not correspond to the information in the bar code.
A particular non-uniform illumination problem occurs when a bar code has a shiny surface. The shiny surface can reflect the light used to illuminate it, causing a region or line of glare to appear on the bar code. This glare increases the difficulty of reading the bar code because the software for processing the images may be unable to compensate for the differing amounts of light emanating from different parts of the bar code. This may result in incorrect readings or having to read the bar code several times in order to obtain an acceptable reading, or may result in parts of the bar code being unreadable.
Particularly susceptible to glare lines are bar codes on curved surfaces or surfaces which are not substantially flat, such as those on the cylindrical containers used for singly-packaged cigarettes.
From the foregoing it is seen that there is a need for improved bar code readers and methods for reading bar codes that reduce the problem of glare and other nonuniformities in illumination.
An apparatus and method for reading a bar code on an object includes a light diffusing cavity and a deflector. The deflector deflects and diffuses light from a light source which may be part of a bar code reader. Preferably the deflector deflects substantially all of the light from the reader, so that none of the light from the light source directly illuminates the bar code. Inner side wall surfaces of the light diffusing cavity redirect the deflected light to indirectly illuminate the bar code. Despite deflecting light from the light source, the deflector allows unhindered passage of light emanating from the bar code to a light detection system which may be part of the bar code reader.
According to an aspect of the invention, an apparatus for use in reading a bar code using a conventional bar code reader includes a housing with respect to which a bar code reader and a bar code may be placed, and having a deflector preventing at least a portion of light emitted by a light source from directly impinging upon the bar code, and at least one surface directing to the bar code at least some of the at least a portion of light.
According to an aspect of the invention, an apparatus for use in reading a bar code includes a deflector for preventing at least a portion of light emitted by a light source from directly impinging upon the bar code, and at least one surface for directing to the bar code at least some of the at least a portion of light.
According to another aspect of the invention, a method for reading a bar code includes indirectly illuminating the bar code by using a deflector between a light source and the bar code, the deflector deflecting at least a portion of source light emanating from the light source; and receiving light emanating from the bar code for decoding.
According to another aspect of the invention, a method for reading a bar code includes indirectly illuminating the bar code by using a deflector between a light source and the bar code, the deflector deflecting at least a portion of source light emanating from the light source; and receiving light emanating from the bar code through an opening in the deflector.
According to yet another aspect of the invention, an apparatus for use in reading a bar code includes a deflector between a light source location and a bar code location, the deflector preventing at least a portion of light emitted at the light source location from directly reaching the bar code location; and at least one surface at least partially in the path of the at least a portion of light, the at least one surface directing at least some of the portion of light to the bar code location.